Who decides on the sentence?
Juries do not sentence you. Only a judge can impose a sentence and only after a conviction by jury, or you plead guilty to the judge.
Judges cannot offer you a sentence. You cannot negotiate with the judge. The judge must first determine whether your guilt has been proven or if your plea of guilty is knowing and voluntary.
The judge is not your friend. The judge cannot help you. The judge cannot advise you. Do not think for a moment that the judge will be lenient because you are in a bad situation.
Think of the judge as an umpire. An umpire will not award the game to one team over another, he can’t. He calls the strikes, calls the fouls, and is there to make sure the rules are followed.
Judges must follow the sentencing law in your jurisdiction. You cannot appeal a judge's sentence unless the sentence is illegal in some way. This rarely happens.